CN106880372B

CN106880372B - Tomography apparatus and method for large-space 3D photographing

Info

Publication number: CN106880372B
Application number: CN201610872037.2A
Authority: CN
Inventors: S.鲍尔; P.库格勒; G.劳里特施; A.梅尔; D.施特罗默
Original assignee: Siemens Healthcare GmbH
Current assignee: Siemens Healthcare GmbH
Priority date: 2015-10-08
Filing date: 2016-09-30
Publication date: 2020-10-13
Anticipated expiration: 2036-09-30
Also published as: US10398390B2; US20170100083A1; CN106880372A; DE102015219520A1

Abstract

The invention relates to a tomography device (R) having a radiation source (Q) and a detector (RD), which is ready to carry out a scan when a rectangular sensor Surface (SF) of the detector (RD) at a distance (SID) from the radiation source (Q) is guided around a track axis (OA) along a circular or spiral first trajectory (BK1Q) while the radiation source (Q) is guided around the track axis (OA) along a circular or spiral second trajectory (BK 2S). The deviation angle (GW) between the central vertical plane (MS) of the sensor plane (SF) and the rotation plane (RE) in which the radiation source (Q) is currently located during scanning has a value greater than 0 DEG and simultaneously less than 90 deg. The invention further relates to a corresponding method (100) for acquiring projection data.

Description

Tomography apparatus and method for large-space 3D photographing

Technical Field

The invention relates to a tomography apparatus with a radiation source and a detector. The tomography apparatus is ready to carry out a scan when the radiation source is guided around the trajectory axis along a first circular or spiral trajectory, when the rectangular sensor surface of the detector is guided around the trajectory axis along a second circular or spiral trajectory spaced apart from the radiation source. Typically the first and second tracks are arranged centrally with respect to each other. The second circular locus is generally located in the plane of rotation of the first circular locus. In a particularly preferred embodiment, the distance of the radiation source from the sensor surface is kept constant, while the sensor surface of the detector is guided along a circular or spiral second trajectory around the trajectory axis. In this case, when the first locus is circular, the second locus is also circular. Furthermore, the two tracks may be identical (but staggered in time from each other). The source and the detector may be fixed on a common moving support, for example a C-arm of its own, or on different moving supports, for example one robot arm each. Optionally, a pattern amplifier is connected to the detector. An option independent of this provides that the detector comprises a graphic amplifier. The tomography apparatus may be, for example, an X-ray tomography apparatus or a fluorescence tomography apparatus.

The invention further relates to a corresponding method for acquiring projection data.

Background

Increasingly high demands are being made on the quality of medical devices in particular in diagnosis and therapy. It is therefore particularly desirable to achieve the object of avoiding health risks and personal injuries as a result of incorrect diagnosis or treatment.

Document DE 10147160C 1 describes a C-arm tomography apparatus with a rectangular detector which is supported so as to be rotatable by 90 ° about a connecting axis relative to the radiation source for achieving, despite the limited size of the detector area: the object of the image to be reconstructed is detected as completely as possible in all rotational directions in the projection acquisition.

Disclosure of Invention

The object of the present invention is to provide a tomography apparatus having a C-arm and a method for acquiring projection data, by means of which apparatus or by means of which 3D recordings can be made in a larger space than in known C-arm tomography apparatuses.

The object is achieved according to the invention by a tomography apparatus having a radiation source and a detector. The tomography apparatus is ready to perform a scan when the radiation source is guided around the trajectory axis along a circular or spiral first trajectory, and when the rectangular sensor surface of the detector, which is at a distance from the radiation source, is guided around the trajectory axis along a circular or spiral second trajectory. The deviation angle (Gierwinkel) between the central vertical plane of the sensor surface and the rotation plane in which the radiation source is currently located during scanning has a value greater than 0 DEG and simultaneously less than 90 deg.

A method for acquiring projection data according to the present invention comprises the following steps. In a first method step, the examination subject is placed between the radiation source and the rectangular sensor surface of the detector. In a second method step, the deviation angle between the central vertical plane of the sensor surface and the rotation plane in which the radiation source is currently located is set to a value greater than 0 ° and less than 90 ° by means of a rotation of the sensor surface about the surface normal of the sensor surface. In a third method step, the radiation source is guided along the circular or spiral first trajectory around the trajectory axis while the sensor surface of the detector is guided along the circular or spiral second trajectory around the trajectory axis. The radiation source is active in at least a plurality of orbital positions for examining the object with radiation transillumination. The second method step can also be carried out before or simultaneously with the first method step.

The idea of the invention is that the deviation angle between the central vertical plane (or central vertical line) of the sensor plane and the rotation plane in which the radiation source is currently located has a value greater than 0 ° and less than 90 °. The maximum effective length of the sensor surface in the direction of rotation is thereby increased without the remaining arrangement and dimensions of the tomography device or the sensor surface having to be changed.

When the diagonal of the sensor surface extends parallel to the plane of rotation, the tomography apparatus is ready to perform a scan, which has the advantage. This arrangement has the same meaning as adjusting the slip angle, in which the effective length of the sensor surface in the direction of rotation has a maximum value.

It is particularly preferred that the tomography apparatus is ready to perform a scan when the diagonal of the sensor plane lies in the plane of rotation. The efficiency of the imaging is usually maximal when the center point of the sensor face is located in the radial plane of the first trajectory. When the slip angle is to be adjusted at the same time (in which the effective length of the sensor surface in the direction of rotation has a maximum value), this has the same meaning as if the diagonal of the sensor surface lies in the plane of rotation.

Independently, a purposeful further development provides that the tomography device is ready to carry out a scan when the rail axis is parallel to the sensor plane. In this orientation of the sensor surface, the radiation angle is at a maximum, which can be detected from the sensor surface into the environment. However, situations are conceivable in which an inclined position of the sensor surface relative to the rail axis is advantageous. For example, by means of the oblique position of the sensor surface relative to the rail axis, a higher resolving power in the direction of the rail axis can be achieved with constant sensor technology.

In the rotation plane, the diameter of the evaluable space can be further enlarged, i.e. the tomographic apparatus is ready to perform a scan when the isocenter (Isozentrum) is guided along a circular third trajectory, the axis of rotation of which is fixed in position relative to the frame of reference of the examination object during the scan.

The extension of the evaluable space can additionally be further extended in that the tomography apparatus is ready to carry out a scan when the isocenter is guided along a helical fourth trajectory, the axis of rotation of which is fixed in position relative to the frame of reference of the examination object during the scan.

When the off angle is greater than 5 ° or greater than 10 ° or greater than 20 °, the tomographic apparatus is ready to perform scanning, which is advantageous. Independently of this, it is advantageous if the tomography apparatus is ready to carry out a scan when the deviation angle is less than 85 °, or less than 80 °, or less than 70 °.

In a particularly preferred embodiment, the tomography apparatus has a C-arm which can be rotated angularly and/or orbitally about an orbit axis and which carries the radiation source at a first end and the detector at its second end, the detector having the sensor surface being supported so as to be rotatable about a surface normal of the sensor surface. The diameter of the evaluation space can thereby be adapted to the current application requirements by means of manual or motor-driven adjustment of the slip angle.

Drawings

The invention is further illustrated below with reference to the accompanying drawings, in which:

figure 1 shows a schematic perspective view of a C-arm tomography apparatus with a radiation source, a detector and a patient table,

figure 2 schematically shows the layout of the sensor face of the detector of figure 1,

figure 3 schematically shows a respective cross-sectional view of a central disk of an evaluable space of a short scan without and with rotation of the sensor surface of the detector,

FIG. 4 shows a schematic diagram of an evaluable space for the arrangement of FIG. 3, where the brightness of a single image point in the view is a measure of the dimension for the cut length of the spatial angle belonging to the respective image point;

FIG. 5 shows respective cross-sectional views of a central disk of an evaluable space of a large-space scan with no rotation of the sensor face of the detector and a displacement of the detector of 310mm (left diagram) and with a displacement of the detector of 390mm (right diagram) with rotation of the sensor face of the detector,

FIG. 6 shows a schematic diagram of an evaluable space for the arrangement of FIG. 5, where the brightness of a single image point in the view is a measure of the dimension for the cut length of the spatial angle belonging to the respective image point;

FIG. 7 shows respective sectional views of a central disk of an evaluable space for a large-space scan with a source-sensor spacing of 900mm with no rotation of the sensor face of the detector and with a displacement of the detector of 310mm (left diagram) and with a displacement of the detector of 390mm (right diagram) with a rotation of the sensor face of the detector,

fig. 8 shows a schematic representation of an evaluable space with the arrangement of fig. 7, wherein the brightness of a single image point in the view is a measure for the size of the cut length of the spatial angle belonging to the respective image point,

fig. 9 shows a schematic diagram of an evaluable space for a large spatial scan with a detector rotation, a source-sensor-spacing of 900mm and a detector displacement of 370mm, the brightness of a single image point in the view being a measure of the dimension for the cut length of the spatial angle belonging to the respective image point,

fig. 10 shows a schematic diagram of an evaluable space for a helical scan with a detector displacement of 390mm at detector rotation, the brightness of a single image point in the view being a measure of the dimension of the cut length for the spatial angle belonging to the respective image point,

fig. 11 shows a schematic diagram of an evaluable space for a helical scan with a detector displacement of 370mm at detector rotation, the brightness of a single image point in the view being a measure of the dimension of the cut length for the spatial angle belonging to the respective image point,

FIG. 12 shows a table of the comparison of the setting of the evaluable space and the diameter of the recommended scanning method, an

Fig. 13 schematically shows a flow of a method for acquiring projection data.

The embodiments illustrated in detail below represent preferred embodiments of the invention.

Detailed Description

Fig. 1 shows a tomography apparatus R with a C-arm CB, a radiation source Q, a detector RD and a patient bed AP. The detector RD has a sensor plane SF.

The following two operating modes are currently used clinically to carry out a 3D scan along a circular trajectory BK1 using a multi-axis C-arm system R. The first mode of operation is called short scan and the second mode is called large spatial scan.

In a short scan, the C-arm performs an angular or orbital rotation around the orbit axis OA by an angle of 180 ° plus the radiation angle SW for obtaining a minimum complete data record for a given geometry. Fig. 1 shows the position of the C-arm CB at the time of angular rotation RO. During orbital rotation RO (not shown in the drawings), C-arm CB is oriented perpendicular to orbital axis OA.

The large spatial scan effects an angular or orbital 360 ° rotation about the orbit axis OA in the direction of rotation RR, wherein the center point MP of the sensor surface SF is offset by half the detector width DB from the central ray ZS of the beam RB (see fig. 2). The diameter DV of the space AV that can be evaluated thereby is enlarged by a factor of approximately 2 in the direction of rotation RR.

According to the clinical workflow, the estimated diameter DV of the space AV is small even in large space scans and cannot cover the entire space of interest (e.g. when scanning the liver of a large patient). At the same time, an appreciable reduction of the extension HV of the space AV in the direction of the track axis OAR (i.e. perpendicular to the direction of rotation RR) is tolerable. There is therefore a need for an application in such a way that the diameter DV of the evaluable space AV is enlarged in the direction of rotation RR.

Current robot C-arm systems R allow many kinds of orbital runs to be used. A method is described below, by means of which the coverage of the side faces for short scans and large-space scans is enlarged by means of a rotation DR of the sensor surface SF about a surface normal FN of the sensor surface SF. In this operating mode, the extension AF of the field of view F is no longer limited in the direction of rotation RR to the length of the longest side of the sensor surface SF. Instead the entire length of the diagonal DS of the sensor plane SF is utilized. This solution can be combined with existing methods and new track runs.

In a short scanning run, the data detection is performed with a rotation of 200 ° (i.e. 180 ° plus a radiation angle SW of 20 °) around the track axis OA for obtaining a minimum complete data recording for the radiation geometry. The sensor surface SF is oriented either in Landscape (Landscape) mode or in Portrait (portal) mode. The rotation RR rotates around the isocenter iz (isozentrum) along a circular trajectory BK 1.

The large spatial scan covers a complete rotation of 360 ° about the track axis OA, wherein the sensor plane SF is displaced by half the extension AS of the sensor plane SF in the direction of rotation RR (meaning the extension AS of the sensor plane SF in the direction of rotation RR). With such a displacement V of the sensor surface SF, the diameter DV of the evaluable space AV is increased by a factor of 2 compared to a short scan. In this operating mode, the sensor surface SF is either in landscape mode or in portrait mode. Instead of moving the sensor plane SF, in practical implementations a rotation is usually effected about the planet axis PA, which is guided about the orbit axis OA along the third circular trajectory BK3 during scanning. The displacement for a large spatial scan is 310mm when the sensor dimensions (dimensions of the sensor plane SF) are 680mm by 480mm, without rotation of the sensor plane SF, whereby the diameter DV of the evaluable space AV increases to 620 mm.

In contrast to the known operating modes, in which the sensor surface SF is either in portrait or in landscape mode, it is proposed according to the invention that the diameter DV of the evaluable space AV is increased by detecting data with the aid of the sensor surface SF which rotates at an angle of departure GW relative to the plane of rotation RE in which the radiation source Q is actually located. In order to maximize the diameter DV of the evaluable space AV, the sensor surface SF is rotated to such an extent that the diagonal DS of the sensor surface SF lies in the rotation plane RE. The preferred deviation angle GW can be calculated with GW arctan (DB/DH), where DB is the width of the sensor field SF (sensor width) and DH is the height of the sensor field SF (sensor height).

In the short scan mode, a rotation of 200 ° about the orbit axis OA is carried out without a detector displacement V for obtaining a minimum complete data record for the cone beam geometry. Circular trajectories BK1, BK2 with a projection matrix of, for example, 200 are used here for the radiation source Q and the sensor field SF. The average angular step is 1.0 ° here. The length of the diagonal DS is about 784mm when the sensor face SF is 680mm by 480 mm. The diameter DV of the evaluable space AV is enlarged by about 26.5% compared to the known diameter DV of the evaluable space AV of 620 mm. Considering the source-patient-distance, which is half of the source-sensor-distance SID (source-to-image distance), the diameter DV of the space AV can be estimated to be 392mm, instead of 310 mm.

The large spatial scan covers a 360 deg. rotation about the orbit axis OA. The circular trajectories BK1, BK2 for the radiation source Q and the sensor field SF contain, for example, a 180 projection matrix, which yields an angular step of 2.0 ° on average. In large-space scanning, the sensor plane SF is displaced by half the width of the sensor plane SF in the direction of rotation RR. The diameter DV of the space AV can thus be estimated to be enlarged by a factor of 2 compared to a short scan. In a given dimension of the sensor face SF, the displacement V is set to 310 mm. When the sensor surface SF is rotated so far that its diagonal DS lies in the plane of rotation RE, the maximum possible displacement V of the sensor surface SF_maxBy means of V_max＝1/2√(DB²+DH²) To calculate.

For the above dimensions of the sensor plane SF, the maximum reasonable displacement V_max392 mm. To ensure complete coverage of the data detection, the displacement V is determined to be 390 mm. The closer the sensor plane SF is to this limit value, the more threshold-related decreases of the extension HV of the evaluable space AV in the track axis direction OAR are.

Fig. 2 shows different displacements V of the sensor surface SF in the direction of rotation RR. In the case of the maximum displacement V, the diameter DV of the evaluable space AV is increased to 620mm or 780mm in the direction of rotation RR. This corresponds to: it can be estimated that the diameter DV of the space AV is increased by about 25.8% in the rotation direction RR.

The rotation DR of the sensor surface SF has the disadvantage of a loss of information, which is greater the further away from the rotation plane RE the information for imaging is. To compensate for this loss, a spiral scan in combination with a rotating sensor plane SF may be used. One embodiment provides 5 complete revolutions, the pitch (pitch) GH being selected to be as small as possible and to be sufficiently large as required. Tests have shown that a pitch (pitch) of 9 mm is ideal in view of the provided probe configuration. It is assumed here that in this configuration the diameter DV of the evaluable space AV remains constant in the direction of rotation RR, while the axial length of the evaluable space AV continues to expand with each rotation.

Instead of implementing a complete helical scan, which is difficult to implement with current systems, alternative data detection modes can also be combined with this mode of operation.

In order to calculate the data integrity of the voxels for the scan, a method for arbitrary discrete detection of the trajectory can be used. The method calculates a three-dimensional evaluable space of the normal to the surface on the cell sphere and intensities between 0 and 1 at the respective voxels. As a result, a three-dimensional image having a preset image size is generated. To speed up the calculation, the image size is determined to be 64 by 64 voxels, and the voxel spacing is 16mm to 4 mm. To improve the display, the evaluation limit value (cut-off value) is set to 0.9. This can be displayed by means of an already implemented "OpenCL Forward Projector", in which the diameter DV of the resulting evaluable space AV is determined. The voxel spacing can be determined to be 1mm by 1mm for the projection.

The left part of fig. 3 shows an image of the central disk ZS of the evaluable space AV for standard short scanning when the sensor plane SF is not rotated DR, while the right part of fig. 3 shows a cross section of the evaluable space AV when the sensor plane SF is rotated, wherein the diagonal DS of the sensor plane SF is arranged in the rotation plane RE. By measuring the diameter DV of the evaluable space AV, an enlargement of 4 pixels of the diameter DV of the evaluable space AV can be observed, since the diagonal DS of the sensor plane SF is arranged in the rotation plane RE. The calculation of the diameter DV of the evaluable space AV is shown in millimeters, which is desirable. For a standard short scan and 384mm, the diameter DV of the complete evaluable space AV reaches 320mm when the diagonal DS of the sensor plane SF is arranged in the rotation plane RE (and the preset voxel spacing is 16 mm). The evaluable space AV thus has a diameter DV that is 64mm larger than when the sensor plane SF is not rotated DR, which means that the diameter DV of the evaluable space AV is increased by 20.0% by arranging the diagonal DS of the sensor plane SF in the plane of rotation.

The reconstruction of the three-dimensional image of fig. 3 results in a field of view F. The left part of fig. 4 shows the field of view F of the short scan when the sensor plane SF is not rotated. The right part of fig. 4 shows a field of view F with a short scan when the sensor plane SF rotates. The (maximum) spread AF of the field of view F of the standard short scan reaches 310mm in the rotation direction RR, while the spread AF of the field of view F of the corrected scan reaches 390mm in the rotation direction RR. This results in an overall difference of 80mm in the direction of rotation RR. The arrangement of the diagonal DS of the sensor surface SF in the rotation plane RE produces an expansion AF of the field of view F of about 25.8% in the rotation direction RR and corresponds precisely to the desired value. The field of view F of the reconstructed image is no longer rectangular but hexagonal.

Fig. 5 shows an interface diagram of an evaluable space AV, which is calculated for two large space scans. The left part of fig. 5 shows a cross-sectional view of the central disk ZS of the evaluable space AV for large-space scanning, when the sensor plane SF is not rotated, but the displacement V of the sensor plane SF is half the detector width (310 mm). The right part of fig. 5 shows a cross-sectional view of the central disk ZS of the evaluable space AV for large-space scanning when the displacement V of the sensor plane SF is half the length (390mm) of the diagonal DS of the sensor plane SF, which is arranged in the rotation plane RE. The calculated maximum reasonable detector displacement V is 390 mm. It can be shown that by the diagonal DS of the sensor plane SF being arranged in the rotation plane RE and the displacement of the sensor plane SF in the rotation direction RR, the diameter DV of the evaluable space AV is increased by 96mm in the rotation direction RR. The diameter of the space AV can be estimated to increase from 576mm to 672mm and by 16.7%.

After the reconstruction of the three-dimensional image, the field of view F shown in fig. 6 is obtained, wherein the left part of fig. 6 shows the field of view F of a standard large-space scan at a displacement V of the sensor plane SF of 310 mm. The right part of fig. 6 shows the field of view F for large spatial scanning when the displacement V of the sensor plane SF is half the length (390mm) of the diagonal DS of the sensor plane SF, which is arranged in the rotation plane RE. The spread AF of the field of view F in the direction of rotation RR is 620mm for a standard scan, where the spread AF of the field of view F reaches 780mm when the diagonal DS is set in the plane of rotation RE. This results in a 25.8% increase and a 160mm increase, which also matches the desired value. In a further observation, it can be seen that the extent HF of the field of view F in the direction of the orbital axis OAR is negatively influenced. The extent HF of the field of view F in the direction of the orbital axis OAR is very small and cannot be formally covered. The extent HF of the field of view F in the direction of the axis of orbit OAR is halved from 240mm to 120 mm.

To achieve a larger diameter DV of the evaluable space AV, the source-sensor-distance SID is reduced to 900 mm. The diameter DV of the evaluable space AV (right part of fig. 7) in operation with a rotation of the sensor surface SF and a simultaneous displacement of 390mm compared with the diameter DV when the sensor surface SF is not rotated but is displaced by 390mm (left part of fig. 7) leads to the result that the diameter DV of the evaluable space AV in the direction of rotation RR is increased by the diagonal DS of the sensor surface SF in the plane of rotation RE from 704mm to 800mm and by 13.6%.

The field of view F after reconstruction is shown in fig. 8. The spread AF of the field of view F of the large-space scan when the diagonal DS of the sensor plane SF is set in the rotation plane RE is 620mm in the rotation direction RR. The extent AF in the direction of rotation RR of the field of view F for large-space scanning is 780mm when the diagonal DS of the sensor field SF is arranged in the rotation plane RE, so that by virtue of the diagonal DS of the sensor field SF being arranged in the rotation plane RE, the maximum expansion of the extent of the field of view F in the direction of rotation RR can be up to 60mm or 25.8%. The extension HF of the new field of view F in the orbit axis direction OAR is still 120mm, which means that a 50% loss of extension HF in the orbit axis direction OAR can be tolerated.

Furthermore, a balance or compromise between the loss of the extension HF of the field of view F in the direction of the orbit axis OAR and the extension of the field of view F in the direction of rotation RR is explored, so that the displacement V of the sensor plane SF in the direction of rotation R is reduced to 370mm in the direction of rotation R. This adjustment should be such that the extension HF of the field of view F in the direction of the axis of orbit OAR is 740 mm. The calculation results in an enlargement of the diameter DV of the evaluable space AV in the direction of rotation RR to 768mm, which still makes it possible to obtain a 9.1% increase.

Fig. 9 shows for this purpose a reconstructed field of view F of an image of the evaluable space AV. The gray frame shows the boundary GF of the field of view F, which is produced by means of the displacement V set by the sensor plane SF. This results in a field of view F where the extension AF is 740mm in the rotation direction RR and the extension HF is 140mm in the track axis direction OAR. The extension HF of the field of view F in the direction of the axis of orbit OAR increases again by 20 mm. Compared to a standard large-space scan, this adjustment still achieves a 19.4% improvement in the rotational direction RR, with a consequent loss in the orbital axis direction OAR of only 41.7%.

In further experiments, instead of circular trajectories, spiral trajectories BK1, BK2 were used for the radiation source Q and the sensor face SF for obtaining a larger extension HV of the evaluable space AV in the direction of the track axis. The dimensions DV, HV of the evaluable space AV remain the same in each revolution, wherein the extension HV of the space AV times the number of revolutions can be evaluated.

Fig. 10 shows the reconstructed field of view F of the evaluable space AV derived therefrom. The spread AF of the field of view F in the rotation direction RR is still 780mm, as expected. 290mm are measured for the extension HF of the field of view F in the direction of the axis of orbit OAR. The five revolutions of the helical scan thus enlarge the field of view F by about 240% compared to the circular scan by the spread HF in the orbital axis direction OAR.

Furthermore, the displacement V of the sensor face SF is again reduced by 20mm to 370 mm. Fig. 11 shows such a result. Compared to the spiral scan with the maximum displacement V, the extension AF of the field of view F in the direction of rotation RR is reduced by 40mm to 740mm, but the expansion of the field of view F in the direction of the track axis OAR amounts to 320 mm. This is 228% larger than a circular scan or 33.33% larger than a large spatial scan when the sensor face SF is not rotated DR.

Comparison of the results shows that the diameter DV of the evaluable space AV in the direction of rotation RR can be increased subject to the loss of the extension HV of the evaluable space in the direction of the rail axis OAR. The new field of view F is not rectangular but hexagonal. It follows that, when the space to be examined has an extension in the direction of the axis of orbit OAR which is as large as in the direction of rotation RR, information is lost at the edges in the direction of the axis of orbit OAR of the space to be examined. If it is known that the view of the space to be examined in the direction of rotation RR is of greater interest than in the direction of the orbit axis OAR, a rotation DR of the sensor plane SF is used for increasing the extent of the field of view F in the direction of rotation RR. A compromise between an expansion of the field of view F in the direction of rotation RR and a reduction of the field of view F in the direction of the orbit axis OAR can be made by adjusting the sensor displacement V or the rotation DR to an intermediate value. If, despite the rotation DR of the sensor surface SF, a greater extension HV of the evaluable space in the direction of the rail axis OAR is still desired, this can be achieved by means of a spiral scan.

The scan geometry produces a certain amount of redundant partial space of the scan, which effect can be reduced by defining the radiation angle SW (by means of calibration) of the ray RS in the direction of the axis of orbit OAR. Only one scanning geometry is thus produced, which closely approximates a diagonal CT scanner with a long, but very narrow sensor plane SF.

The table shown in fig. 12 contains a comparison of the results for the isocenter IZ at 600 mm. In this table, F-o-V represents the field of view F, which is derived by reconstruction. The numerical values for a helical scan refer to a scan having five revolutions.

When the source-sensor spacing SID is 1200mm and the rotation DR of the sensor diagonal DS is in the rotation plane RE, and the other conditions for the scanning mode "short scan" and "large spatial scan" are the same, the spread AF of the field of view F in the rotation direction RR is increased by 25.8%, and at the same time the spread HF of the field of view F in the track axis direction OAR is reduced by 50%. By means of an additional reduction of the source-sensor spacing SID to 900mm, the extension AF of the field of view F in the direction of rotation RR can be increased by a further 128mm, i.e. by a further 13.6%.

In a large spatial scanning mode (with the sensor diagonal DS lying in the rotation plane RE), a 20mm reduction in the displacement V of the sensor face SF results in a reduced pin loss of only 41.7%, not 50%. The increase in the diameter DV of the evaluable space AV is then 9.1%, with an extension AF of the field of view F in the direction of rotation RR of 19.4%. In order to increase the field of view F in the direction of the orbit axis OAR, by means of which the extent AF in the direction of rotation RR is as large as in the circular trajectory BK1, but the extent HF of the field of view F in the direction of the orbit axis OAR is proportional to the number of rotations, helical trajectories BK1, BK2 can be used for the radiation source Q and the sensor field SF. With a maximum displacement V of 390mm and five rotations, the field of view is enlarged to 290 mm. With a compromise of-20 mm by means of the detector displacement, the extension AF of the field of view F can be made up to 320mm in the direction of rotation RR, which means an increase of 33.3% compared to a large spatial scan.

The rotation DR of the sensor face SF therefore provides more accurate results than the known scanning methods in combination with the above-described scanning patterns. This applies in particular to imaging examinations of long, narrow spaces.

The method 100 for acquiring projection data shown in fig. 13 comprises the following steps. In a first method step 110, the examination subject UO is located between the radiation source Q and the rectangular sensor surface SF of the detector RD. In a second method step 120, a deviation angle GW between a central vertical plane MS of the sensor surface SF and a rotation plane RE (in which the radiation source Q is currently located) is set to a value greater than 0 ° and less than 90 ° by means of a rotation DR of the sensor surface SF about a surface normal FN of the sensor surface SF. In a third method step 130, radiation source Q is guided along a circular or spiral first trajectory BK1Q about an axis of trajectory OA, while sensor field SF of detector RD is guided along a circular or spiral second trajectory BK2S about axis of trajectory OA. The radiation source Q is active in at least a plurality of orbital positions OP for the transillumination of the object UO with radiation. The second method step 120 can also be carried out before or simultaneously with the first method step 110. In a particularly preferred embodiment, the distance SID of the radiation source Q from the sensor plane SF of the detector RD remains constant when the sensor plane SF is guided along a circular or spiral second trajectory BK2S about the trajectory axis OA.

The invention also relates to a tomography apparatus R with a radiation source Q and a detector RD, which is ready to carry out a scan when the radiation source Q is guided along a circular or spiral-shaped first trajectory BK1Q around an orbit axis OA. In synchronism with this, the rectangular sensor surface SF of the detector RD, which has a distance SID from the radiation source Q, is guided along a circular or spiral-shaped second trajectory BK2S about the trajectory axis OA. The deviation angle GW between the central vertical plane MS of the sensor plane SF and the rotation plane RE in which the radiation source Q is currently located during scanning has a value greater than 0 ° and at the same time less than 90 °.

Claims

1. A tomographic apparatus (R) with a radiation source (Q) and a detector (RD), which is ready to carry out a scan when a rectangular sensor plane (SF) of the detector (RD) at a distance (SID) from the radiation source (Q) is guided around a track axis (OA) along a circular or spiral-shaped second trajectory (BK2S) while the radiation source (Q) is guided around the track axis (OA) along a circular or spiral-shaped first trajectory (BK1Q),

characterized in that the deviation angle (GW) between a central vertical plane (MS) of the sensor plane (SF) and a rotation plane (RE) in which the radiation source (Q) is currently located during scanning has a value greater than 0 DEG and simultaneously less than 90 DEG, wherein the sensor plane (SF) is displaceable by half the extension of the sensor plane (SF) in the direction of rotation of the rotation plane.

2. A tomography apparatus (R) as claimed in claim 1, characterized in that during scanning the Diagonal (DS) of the sensor plane (SF) extends parallel to the plane of Rotation (RE).

3. A tomography apparatus (R) as claimed in claim 2, characterized in that during scanning the Diagonal (DS) of the sensor plane (SF) lies in the plane of Rotation (RE).

4. A tomography apparatus (R) as claimed in claim 1, characterized in that during scanning the track axis (OA) is parallel to the sensor plane (SF).

5. The tomography apparatus (R) as claimed in claim 1, characterized in that during the scanning the Isocenter (IZ) is guided along a circular third trajectory (BK3), wherein the axis of rotation (RA2) of the circular third trajectory (BK3) is positionally fixed relative to the frame of reference (BS) of the examination object (UO) during the scanning.

6. The tomography apparatus (R) as claimed in claim 1, characterized in that during the scanning the Isocenter (IZ) is guided along a spiral-shaped fourth trajectory (BK4), wherein the axis of rotation (RA2) of the spiral-shaped fourth trajectory (BK4) is positionally fixed relative to the frame of reference (BS) of the examination object (UO) during the scanning.

7. A tomography apparatus (R) as claimed in claim 1, characterized in that the deviation angle (GW) is greater than 5 ° during scanning.

8. A tomography apparatus (R) as claimed in claim 1, characterized in that the deviation angle (GW) is less than 85 ° during scanning.

9. The tomography apparatus (R) as claimed in claim 1, characterized in that the tomography apparatus (R) has a C-arm (CB) which can be rotated angularly and/or orbitally about an Orbit Axis (OA) and which carries the radiation source (Q) at its first end (E1) and the detector (RD) at its second end (E2), wherein the detector (RD) with the sensor plane (SF) is rotatably supported about a plane normal (FN) of the sensor plane (SF).

10. A method (100) of acquiring projection data, wherein the method (100) comprises:

-placing (110) an examination object (UO) between a radiation source (Q) and a rectangular Sensor Face (SF) of a detector (RD);

-the deviation angle (GW) between the central vertical plane (MS) of the sensor plane (SF) and the rotation plane (RE) in which the radiation source (Q) is currently located is adjusted (120) to a value greater than 0 ° and less than 90 ° by means of a rotation (DR) of the sensor plane (SF) about the plane normal (FN) of the sensor plane (SF); wherein the sensor Surface (SF) is displaced in the direction of rotation of the rotation plane, the displacement being at most half the extension of the sensor Surface (SF);

-the radiation source (Q) is guided around the trajectory axis (OA) along a circular or spiral first trajectory (BK1Q) while a sensor plane (SF) of the detector (RD) having a distance (SID) from the radiation source (Q) is guided (130) around the trajectory axis along a circular or spiral second trajectory (BK2S), wherein the radiation source (Q) is active in at least a plurality of trajectory positions (OP) for transillumination of the object (UO) with Radiation (RS).